A diaphragm type magnetic transducer or loud speaker must have certain basic components including a diaphragm with a vibratable area to which signal conducting conductors are secured. The conductors may be round wire, or may be foil, or may be metallic film etched away into conductor shaped strips. The transducer must also include a source of magnetic fields which project to the diaphragm so that the runs of conductor wire are embraced in the magnetic field such that when an audio frequency signal is applied to the conductor, the vibratable area of the diaphragm will vibrate in synchronism with the frequency of the signal applied and produce sounds with the desired magnitude and frequency.
Typically, a magnetic backing adjacent the diaphragm is the source of the magnetic field and has an apertured soft iron plate spaced from the diaphragm and carrying a multiplicity of elongate magnet strips spaced from each other and laid upon the plate. The magnetized strips are related to one another so that their magnetic field will project from the faces of the magnetized strips to the diaphragm and conductors thereon.
Typical diaphragm type magnetic speakers have been illustrated and described in detail in prior U.S. Pat. No. 3,674,946 and 3,929,499. In the earlier patent, the magnetized strips were parts of a panel or sheet of magnetic matieral; and in the later patent; the magnetized strips were physically shaped as strips of the magnetic material. Accordingly, it is clear that such magnetized strips may take various forms.
All of the known prior diaphragm type magnetic speakers have used diaphragms of film type material which are anchored securely around their peripheries to the frame which is rigid with the magnetic backing. In many such transducers, the diaphragm is stretched very tight, but within the elastic limits of the film material. In some instances, the film type diaphragm has been left rather loose. However, in the prior art, the vibratable areas of the diaphragm in such speakers have consistently been caused to flex by reason of the interrelated function of the signal currents flowing through the wires on the diaphragm, together with the magnetic fields produced by the magnetized strips in the magnetic backing. The central portions of the vibratable areas have a very significant movement or excursion away from the normal position in response to the application of signal current in the conductors; but on the other hand, the edge portions of the vibratable areas have remained essentially stationary. As a result, the central portions of the vibratable areas contributes more to the production of sound as compared to the edge portions. Therefore, because the sounds produced in the bass and mid-range frequencies are produced mainly by the central portions of the diaphragm, there is a definite limitation on the magnitude of sounds produced.